This study was designed to evaluate the use of a cold crystalloid intermittent cerebral perfusion, cerebroplegia, for the preservation of cerebral high energy phosphates during a two hour period of hypothermic total circulatory arrest and reperfusion. NMR spectroscopy was utilized to record changes in cerebral ATP, PCR, and intracellular pH. Cardiopulmonary bypass (CPB) was employed to achieve hemodynamic stability during cooling and reperfusion. Sheep (20-35 kg) were divided into 2 groups. Group I received no cerebroplegia and served as the control group. Group II received cerebroplegia. No significant differences were present between the groups prior to arrest. ATP, PCR, and pH were maintained higher in the Group II animals for all points during the arrest period and until 60 minutes following reperfusion.(p less than .05) For the remaining three hours of reperfusion no differences were noted. EEG activity returned after 30 minutes of reperfusion in Group II compared to 120 minutes in Group I.(p less than .05). We have developed a system for the NMR evaluation of cerebral high energy phosphate changes during hypothermic total circulatory arrest and reperfusion using CPB in large animals. Cerebral high energy phosphates and pH are maintained during the arrest period with the administration of cerebroplegia. The rapid return of the EEG signal in the cerebroplegia animals suggests protection was achieved, however further studies must be done to assess the benefits of cerebroplegia in animals that are recovered for functional neurological evaluation.